B12-cell Division And Reproduction Flashcards
Chromosome
Long thread of condensed DNA
Gene
Sections of a chromosome that carry specific information
Alleles
Different versions of genes, specific characteristic
Genotype
The specific combination of genes/alleles that an individual has is called their
Phenotype
The physical presentation of the genes/alleles is called the
Heterozygous
Different alleles one dominant and recessive(carrier)
Homozygous
Same alleles can be both recessive or dominant
In multicellular organisms
cell division (called mitosis) is needed for… replacing old cells and growing (repairing tissues as well)
In unicellular organisms
this sort of cell division is needed for… asexual reproduction.
Meiosis
Making eggs(and sperm)[gametes]for sexual reproduction
Mitosis
Making identical 2
What are the 2 different ways of reproducing
Asexual and sexual reproduction
Asexual reproduction
only involves 1parent, cells divide MITOSIS gives rise to identical offspring or clone so genetic material is identical to parent and each other, cells of your body reproduce asexually all the time but very common in smallest animals and plant, and in fungi and bacteria also larger plants e.g.daffodils
Sexual reproduction
involves 2 parents male and female sex cell these gametes fuse together to form a zygote to create a new individual formed special form cell division MEIOSIS each cell has half amount pf chromosomes so when formed has full amount so inherit genetic information from both parents which is key to long term survival and takes place living things ranging single celled organisms to humans in plants gametes=eggs+pollen in animals gametes=egg cell+sperm
Fertilisation and variation
More variation is added when fertilisation takes place each sex cell has a single set of chromosomes(23) when joined the single new cell has a full set of chromosomes(46) the combination of genes on the chromosome of every newly fertilised egg is unique once complete it starts to divide by mitosis to form a new individual as number of cells increase rapidly and cells start to differentiate. In sexual reproduction by meiosis the combination of genes in the new pair of chromosomes will contain different forms of the same genes (alleles) from each parent. Unlike asexual reproduction by mitosis where there is no variation in genetic material.
Meiosis steps
- The cell contains pairs of chromosomes. In humans there are 46chromosomes(23pairs). 1 chromosome in each pair comes from the father and 1from the mother, each chromosome in the pair is the same length.
- A copy is made of each chromosome. The original and the copy stay together.
- The chromosome pairs line up down the centre of the cell. The pair from the father matches up with the corresponding pair from the mother.
- The chromosome pairs separate and move to opposite ends of the cell. This is the same as a mitotic division resulting in 23pairs of chromosomes in each new nucleus.
- The chromosome pairs now line up again in preparation for a second division. Their second division separates each original chromosome from its copy so that each new cell has 23 chromosomes. The new cells that form are called gametes.
- 4new haploid cells are formed each containing 23 chromosomes. In males these are sperm and in females these are ova (eggs). Each new cell has a unique set of genes.
- the sperm swims to the ovum and sperm’s head enters the ovum. The 2 nuclei merge to produce a fertilised egg containing 46chromosomes that can grow by mitotic division to form an embryo
When does mitosis happen
This type of cell division occurs during growth and repair
Where does mitosis happen
Takes place in all cells apart from gametes
Mitosis how many cells
This type of cell division produces 2 daughter cells
Mitosis how many chromosomes
The daughter cells have the same number of chromosomes as the parent
Mitosis variation between cells
The daughter cells are clones and are genetically identical to the parent
When does meiosis happen
This type of cell division occurs during the production of gametes (sex cells)
Where does meiosis happen
This takes place in the reproductive organs
Meiosis how many cells
This type of cell division produces 4 gametes
Meiosis how many chromosomes
The daughter cells have half as many chromosomes as the parent
Meiosis variation between cells
The daughter cells are genetically different from each other and the parent cell
Info about mitosis
Chromosome replicate, which copies the genetic info
Produces genetically identical cells
2daughter cells produced
Occurs during growth and asexual reproduction
Only 1 cell division occurs
Info about meiosis
4daughter cells produced
1copy of each chromosome (a chromatid)goes to each of the new daughter cells
Occurs in the formation of gametes during sexual reproduction
Only 1/2 of the chromosomes go to each of the new daughter cells
Daughter cells are all genetically different
2 cell division occur
Process when 2 human gametes join together
Fertilisation
The human genome project
was one of the major biological programmes of the
last 20 years. At the outset biologists believed that sequencing all human genes
could provide answers to many questions, such as the causes of some diseases
and the origin of some species
What is a genome
The entire genetic material of the organism
In 1990s biologists started the human genome project the aim was
To sequence a genome of a person
How has the human genome project been extended
Since the initial human genome was read scientists have carried on with the work and the aim is to find out as much as possible about human DNA. As they have now sequenced the genomes of 1000people and are now busy with the current 100,000 genomes projects and even other organisms. Because there is still a lot to find out and there are many reasons why they feel it is worthwhile like understanding inherited diseases more.
advantages of the scientists being organised into teams
around the world to work on the human genome project.
It means that thousands of people all across the world are experimenting and working together for the same goal with different people doing different things.
how scientists used genome sequencing techniques (such as the
human genome project) to establish a classification relationship between two
species.
Because they sequence genomes of hundreds of different species of organisms and use the similarities and differences between two species to help them work out the relationship between the two different species.
The benefits of the human genome project
Understand inherited disorders so the more chance of overcoming through medicines or repairing the faulty genes, the more we likely we are to predict the risk for an individual so they can make lifestyle choices to reduce this risks and finding the best treatment for things like cancer and human evolution and history to trace migration patterns from our ancient history and early members of the human family tree.
A capital letter is always used to refer to the
‘Dominant allele’
A lower case letter refers to the
‘Recessive’ allele
Genetic screening
Cells can be taken from an embryo/foetus and tested or ‘screened.’
These processes check for alleles that cause genetic disorders.
This can be ‘pre-implantation’by screening embryos for faulty alleles during IVF, or it can be post-implantation (e.g.amniocentesis)
What is amniocentesis
Involves taking some fluid from around the developing fetus at around 15-16weeks of pregnancy this fluid contains fetal cells, which can then be used for genetic screening
How are amniocentesis and chorionic villus sampling similar
They both have a risk of a miscarriage but are currently the 2 main methods used to obtain fetal cells for screening which they both do as well
What is chorionic villus sampling
Involves taking a small sample of tissue from the developing placenta earlier between 10 and 12weeks this again provides fetal cells to screen
advantages and disadvantages to offering embryo screening to all pregnant couples:
Although screening is very expensive if a couple have a child affected by a genetic disorder it can be very costly for society to provide health care. But it helps the parents to be prepared because if they are going to have a child with a genetic disorder at least they would know how to get prepared for it and it wouldn’t be a shock. They can also make the choice whether or not to terminate a pregnancy although this is never an easy decision it will have a huge impact on their lives and if they are young especially this will affect them a lot and it may cause ‘too’ much suffering to a life ‘not worth’ living. Some people also are concerned that genetic screening would give rise for ‘designer babies’ with desirable attributes instead of having a normal baby. Also their are risks associated as the processes used to collect cells from a developing fetus increase the risk of miscarriage and screening procedure although they are becoming more reliable and accurate they can give a false positive or false negative result leading to a healthy fetus being miscarried, the termination of a healthy pregnancy or unexpected birth of a child with a genetic disorder.
